Object-shape generation method, object-shape generation apparatus, and program

ABSTRACT

Even in a situation in which an image of the back side of an object cannot be captured, the shape of the object can be generated with high accuracy. For individual images captured from the circumference of an object, projection regions projected in an area from the surface of projection in a projective space to a projective plane that is distant from the surface of projection by a predetermined length in a depth direction in a case where the object reflected in the individual images is projected to the projective space from viewpoint positions of the individual images are detected. A portion common to the individual detected projection regions is extracted.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to and claims the benefit of priority fromJapanese Patent Application No. PCT/JP2008/052908, filed on Feb. 14,2008, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an object-shape generation method, anobject-shape generation apparatus, and a program, and is suitablyapplied, for example, to biometrics authentication.

BACKGROUND ART

Biometrics authentication is a method for identifying a person by usingan identification target of the living body of the person. Blood vesselsof a finger are one identification target of a living body.

For example, an authentication apparatus that generates athree-dimensional image by combining images of different sides of afingertip and uses the three-dimensional image as an identificationtarget has been suggested (for example, see Patent Document 1).

-   Patent Document 1: Japanese Unexamined Patent Application    Publication No. 2002-175529.

Incidentally, an object-shape generation method called a view-volumeintersection method (Shape From Silhouette method) exists. Theview-volume intersection method is a method for generating, inaccordance with images of an object from a plurality of viewpoints,positional information of a camera, and the like, the shape of thetarget object by causing a region in which all the silhouettes in theindividual images intersect with each other within a target space toremain as an object region.

When a three-dimensional blood vessel image is generated using theview-volume intersection method, compared with a two-dimensional bloodvessel image (entire-circumference development image), the number ofparameters serving as identification targets increases. Hence, it isconsidered that the authentication accuracy improves.

However, portions of a living body other than blood vessels are nothollow and are occupied by individual tissues such as fat. Therefore,for example, as shown in FIG. 1, an optical image pickup camera mightnot be able to project a blood vessel portion existing on the back sideof an image pickup surface.

In this case, with the view-volume intersection method, a blood vesselportion on the back side of the image pickup surface that is notprojected to the image pickup surface is not a region in which all thesilhouettes in individual images intersect with each other within atarget space. Thus, the region does not remain as an object region. As aresult, there is a problem in that a shape different from that of theactual blood vessel may be generated.

DISCLOSURE OF INVENTION

The present invention has been made taking into account theabove-described points and provides an object-shape generationapparatus, an object-shape generation method, and a program that arecapable of generating the shape of an object with high accuracy even ina situation in which an image of the back side of the object cannot becaptured.

In order to achieve the object, an object-shape generation methodaccording to the present invention includes a first step of detecting,for individual images captured from the circumference of an object,projection regions projected in an area from the surface of projectionin a projective space to a projective plane that is distant from thesurface of projection by a predetermined length in a depth direction ina case where the object reflected in the individual images is projectedto the projective space from viewpoint positions of the individualimages; and a second step of extracting a portion common to theindividual detected projection regions.

In addition, an object-shape generation apparatus according to thepresent invention includes a work memory; and an image processing unitthat executes image processing by using the work memory. The imageprocessing unit detects, for individual images captured from thecircumference of an object, projection regions projected in an area fromthe surface of projection in a projective space to a projective planethat is distant from the surface of projection by a predetermined lengthin a depth direction in a case where the object reflected in theindividual images is projected to the projective space from viewpointpositions of the individual images, and extracts a portion common to theindividual detected projection regions.

Furthermore, a program according to the present invention causes acontrol unit controlling a work memory to execute processing includingdetecting, for individual images captured from the circumference of anobject, projection regions projected in an area from the surface ofprojection in a projective space to a projective plane that is distantfrom the surface of projection by a predetermined length in a depthdirection in a case where the object reflected in the individual imagesis projected to the projective space from viewpoint positions of theindividual images, and extracting a portion common to the individualdetected projection regions.

As described above, according to the present invention, instead ofextracting a portion common to silhouette regions projected in thedeepest area of the projective space as a stereoscopic image of a bloodvessel, a portion common to silhouette regions projected to an area fromthe surface of projection in the projective space to a projective planethat is distant from the surface of projection by a predetermined lengthin the depth direction is extracted as a stereoscopic image of a bloodvessel. Thus, the view volume can be extracted while attention is paidto a surface portion of an object serving as an image pickup target. Asa result, an object-shape generation method, an object-shape generationapparatus, and a program that are capable of generating the shape of anobject with high accuracy even in a situation in which an image of theback side of the object cannot be captured can be realized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(A) is a schematic diagram showing an image pickup direction side(the front side of an object) for explaining a problem in a view-volumeintersection method, and FIG. 1(B) is a schematic diagram showing a sideopposite the image pickup direction side (the back side of the object)for explaining the problem in the view-volume intersection method.

FIG. 2 is a block diagram showing the configuration of an authenticationapparatus according to the embodiment.

FIG. 3 is a schematic diagram showing the transition of the state of arotating finger.

FIG. 4 is a schematic diagram showing the relationship between an imagepickup surface and a blood vessel inside an image.

FIG. 5 is a block diagram showing the functional configuration of acontrol unit.

FIG. 6 is a schematic diagram for explaining calculation of a rotationcorrection amount.

FIG. 7 is a schematic diagram showing images before and after embossingprocessing is performed.

FIG. 8 is a schematic diagram for explaining a motion amount calculationprocess.

FIG. 9 is a schematic diagram showing the brightness state of a bloodvessel in an image after embossing processing is performed.

FIG. 10 is a schematic diagram showing the transition of the state ofbrightness by a blood vessel extraction process.

FIG. 11 is a schematic diagram for explaining equalization of thebrightness state.

FIG. 12 is a schematic diagram showing a voxel space.

FIG. 13 is a flowchart showing an object-shape generation process.

FIG. 14 is a schematic diagram for explaining detection (1) of asilhouette region.

FIG. 15 is a schematic diagram for explaining the positionalrelationship between individual images placed around a voxel space.

FIG. 16 is a schematic diagram for explaining detection (2) of asilhouette region.

FIG. 17 is a schematic diagram showing the extraction state of asilhouette region.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment to which the present invention is appliedwill be explained in detail with reference to the drawings.

(1) Entire Configuration of Authentication Apparatus According to thisEmbodiment

FIG. 2 shows the entire configuration of an authentication apparatus 1according to this embodiment. The authentication apparatus 1 isconfigured by connecting each of an operation unit 11, an image pickupunit 12, a memory 13, an interface 14, and a notification unit 15 to acontrol unit 10 through a bus 16.

The control unit 10 is configured as a computer including a CPU (CentralProcessing Unit) controlling the entire authentication apparatus 1, aROM (Read Only Memory) in which various programs, setting information,and the like are stored, and a RAM (Random Access Memory) as a workmemory for the CPU.

An execution command COM1 for a mode in which blood vessels of a user tobe registered (hereinafter, this will be referred to as a registrant) isregistered (hereinafter, this will be referred to as a blood vesselregistration mode) or an execution command COM2 for a mode in whichidentification of a registrant is determined (hereinafter, this will bereferred to as an authentication mode) is supplied from the operationunit 11 to the control unit 10, in accordance with a user operation.

The control unit 10 is configured to determine, in accordance with theexecution command COM1 or COM2, a mode to be executed, control the imagepickup unit 12, the memory 13, the interface 14, and the notificationunit 15 in an appropriate manner in accordance with a programcorresponding to the determination result, and execute the blood vesselregistration mode or the authentication mode.

The image pickup unit 12 adjusts the position of a lens in an opticalsystem, the aperture of a diaphragm, and the shutter speed (exposuretime) of an image pickup element, in accordance with an exposure value(EV (Exposure Value)) specified by the control unit 10.

The image pickup unit 12 also performs A/D (Analog/Digital) conversionof image signals, as image pickup results at the image pickup element,sequentially output from the image pickup element at predeterminedintervals, and transmits image data obtained as the conversion resultsto the control unit 10.

Furthermore, the image pickup unit 12 drives a near infrared ray lightsource during a period of time specified by the control unit 10, andapplies near infrared rays, which are specifically absorbed by bloodvessels, to a position specified as an image pickup target (hereinafter,this will be referred to as an image pickup position).

In a case where a living body portion is placed at the image pickupposition, a near infrared ray passing inside the living body portion isincident, as light that projects blood vessels, to the image pickupelement by the optical system and the diaphragm, and an image of theblood vessels inside the living body is formed on an image pickupsurface of the image pickup element. Consequently, in this case, theblood vessels are reflected in an image obtained as the image pickupresult by the image pickup unit 12.

The memory 13 includes, for example, a flash memory. The memory 13 isconfigured so that data specified by the control unit 10 is stored inthe memory 13 or read from the memory 13.

The interface 14 is configured to transmit and receive various data toand from an external apparatus connected through a predeterminedtransmission line.

The notification unit 15 includes a display section 15 a and a soundoutput section 15 b. The display section 15 a displays, on a displayscreen, contents based on display data supplied from the control unit 10in the form of letters or diagrams. Meanwhile, the sound output section15 b is configured to output, from a speaker, sound based on sound datasupplied from the control unit 10.

(2) Blood Vessel Registration Mode

Next, the blood vessel registration mode will be explained. Whendetermining the blood vessel registration mode as a mode to be executed,the control unit 10 changes the operation mode to the blood vesselregistration mode and causes the notification unit 15 to issue anotification indicating that there is a need to place a finger at animage pickup position and to rotate the finger on the curved ventralsurface of the finger. At the same time, the control unit 10 causes theimage pickup unit 12 to operate.

In this state, in a case where, for example, as shown in FIG. 3, thefinger is rotated around the finger circumference (the ventral surface,lateral surfaces, and dorsal surface of the finger), the image pickupunit 12 continuously captures images of blood vessels inside the fingeraround the finger circumference as images from a plurality ofviewpoints, for example, as shown in FIG. 4.

The control unit 10 generates, as an image pickup result by the imagepickup unit 12, a stereoscopic image of blood vessels in accordance withthe images sequentially supplied from the image pickup unit 12, andregisters values representing the shape of the stereoscopic image of theblood vessels (hereinafter, these will be referred to as blood vesselshape values) as data to be registered (hereinafter, this will bereferred to as registration data) by storing the registration data inthe memory 13.

The control unit 10 is configured to be capable of executing the bloodvessel registration mode, as described above.

(3) Authentication Mode

Next, the authentication mode will be explained. When determining theauthentication mode as a mode to be executed, the control unit 10changes the operation mode to the authentication mode and causes thenotification unit 15 to issue a notification indicating that there is aneed to place a finger at an image pickup position and to rotate thefinger on the curved ventral surface of the finger. At the same time,the control unit 10 causes the image pickup unit 12 to operate.

The control unit 10 generates, as an image pickup result by the imagepickup unit 12, a stereoscopic image of blood vessels in accordance withimages sequentially supplied from the image pickup unit 12, and extractsblood vessel shape values of the blood vessels, as in the blood vesselregistration mode. The control unit 10 is configured to verify theextracted blood vessel shape values against blood vessel shape valuesstored as registration data in the memory 13 and to determine, inaccordance with the verification result, whether or not the owner of thefinger can be approved as a registrant.

Here, if it is determined that the owner of the finger cannot beapproved as a registrant, the control unit 10 causes the display section15 a and the sound output section 15 b to issue, in a visual andauditory manner, a notification indicating that the owner of the fingercannot be approved as a registrant. Meanwhile, if it is determined thatthe owner of the finger can be approved as a registrant, the controlunit 10 transmits, to an apparatus connected to the interface 14, dataindicating that the owner of the finger has been approved as aregistrant. This apparatus is triggered by the data indicating that theowner of the finger has been approved as a registrant, and performs, forexample, predetermined processing to be performed at the time whenauthentication is successful, such as closing a door for a certainperiod of time or cancelling a restricted operation mode.

The control unit 10 is configured to be capable of executing theauthentication mode, as described above.

(4) Blood Vessel Shape Value Extraction Process

Next, the details of a blood vessel shape value extraction process bythe control unit 10 will be specifically explained. In terms offunctions, this process can be divided into an image rotation unit 21, ablood vessel extraction unit 22, a motion amount calculation unit 23,and a three-dimensional image generation unit 24, as shown in FIG. 5.Hereinafter, the image rotation unit 21, the blood vessel extractionunit 22, the motion amount calculation unit 23, and thethree-dimensional image generation unit 24 will be explained in detail.

(4-1) Image Rotation Process

The image rotation unit 21 rotates and corrects images from a pluralityof viewpoints so that the direction of a finger reflected in theindividual images is defined as a reference direction.

An example of a rotation method by the image rotation unit 21 will beexplained. The image rotation unit 21 places an optical filter thattransmits only visible light at a predetermined position on an opticalaxis for each period that is different from an image pickup period, andobtains, with a predetermined interval relative to an image of a bloodvessel to be captured (hereinafter, this will be referred to as a bloodvessel image), an image of a finger to be captured (hereinafter, thiswill be referred to as a finger image) as a rotation amount to becalculated.

Incidentally, a blood vessel image is an image formed on an image pickupelement by using near infrared light as image pickup light, and a fingerimage is an image formed on an image pickup element by using visiblelight as image pickup light.

For example, as shown in FIG. 6, in a case where a finger image isobtained (FIG. 6(A)), after extracting the region of a finger reflectedin the finger image (FIG. 6(B)), the image rotation unit 21 extractspoints constituting the silhouette of the finger (hereinafter, thesewill be referred to as finger silhouette points) (FIG. 6(C)).

In addition, the image rotation unit 21 extracts, by performingweighting by Hough transform or the like, points corresponding tohorizontal silhouette lines as points constituting a knuckle(hereinafter, these will be referred to as knuckle points) from amongthe finger silhouette points (FIG. 6(D)), and identifies a knuckleportion line (hereinafter, this will be referred to as a knuckle line)JNL in accordance with the knuckle points (FIG. 6(E)).

Then, the image rotation unit 21 obtains the angle θx of the knuckleline JNL with respect to a line LN in a transverse direction in theimage as the rotation correction amount for a blood vessel image (FIG.6(E)), and rotates and corrects each blood vessel image captured untilthe next finger image is obtained, in accordance with the rotationcorrection amount.

As a result, in this example, in blood vessel images from a plurality ofviewpoints, the longitudinal direction of the finger reflected in theblood vessel images is made the same as the longitudinal direction ofthe images.

As described above, the image rotation unit 21 performs the imagerotation process on a plurality of image data items sequentiallyreceived from the image pickup unit 12 as blood vessel images from aplurality of viewpoints continuously captured along the fingercircumference, and transmits the image data obtained as the processresults to the blood vessel extraction unit 22.

(4-2) Blood Vessel Extraction Process

The blood vessel extraction unit 22 extracts a blood vessel portionreflected in a blood vessel image. An example of an extraction method bythe blood vessel extraction unit 22 will be explained. In the bloodvessel extraction unit 22, an embossing section 22A performs embossingprocessing using a differentiation filter, such as a Gaussian filter ora Log filter, on the image data received from the image rotation unit 21so that blood vessels are embossed on the image.

Now, images before and after embossing processing is performed are shownin FIG. 7. In a blood vessel image before embossing processing isperformed (FIG. 7(A)), the boundary between blood vessels and the otherportions is vague. Meanwhile, in a blood vessel image after embossingprocessing is performed (FIG. 7(B)), the boundary becomes clear. As isclear from FIG. 7, blood vessels are highlighted by the embossingprocessing by the embossing section 21. As a result, blood vessels andthe other portions can be clearly distinguished from each other.

In addition, in the blood vessel extraction unit 22, a binarizingsection 22B performs binarizing processing on the image data on whichblood vessels are embossed with reference to a set brightness so thatthe image data is converted into a binary blood vessel image(hereinafter, this will be referred to as a binary blood vessel image),and transmits image data obtained as the processing result to thethree-dimensional image generation unit 24.

(4-3) Motion Amount Calculation Process

The motion amount calculation unit 23 calculates a motion amount inaccordance with blood vessels reflected in blood vessel images from aplurality of viewpoints continuously captured along the fingercircumference.

An example of a calculation method by the motion amount calculation unit23 will be explained. The motion amount calculation unit 23 calculates,in accordance with an optical flow, the amount of motion betweencorresponding portions in blood vessels reflected in a first bloodvessel image received from the blood vessel extraction unit 22 and in asecond blood vessel image received from the blood vessel extraction unit22 prior to reception of the first blood vessel image. Hereinafter, thefirst blood vessel image will be referred to as the current image, andthe second blood vessel image will be referred to as the precedingimage.

That is, for example, as shown in FIG. 8(A), the motion amountcalculation unit 23 determines a point of interest AP in the currentimage IM1 (hereinafter, this will be referred to as a point ofinterest), and identifies the brightness of a block ABL of (m×n) pixelscentered on the point of interest AP (hereinafter, this will be referredto as a block of interest).

Then, as shown in FIG. 8(B), the motion amount calculation unit 23searches, from the preceding image IM2, for a block having thebrightness that is least different from the brightness in the block ofinterest ABL, and obtains, by defining the center of a found block RBLas a point XP corresponding to the point of interest AP (hereinafter,this will be referred to as a corresponding point), a position vector(V_(x),V_(y)) from a position AP′ corresponding to the point of interestAP to the corresponding point XP.

The motion amount calculation unit 23 searches, from the preceding imageIM2, for blocks corresponding to a plurality of blocks of interest inthe current image IM1, as described above. At the same time, the motionamount calculation unit 23 calculates the average of individual positionvectors between centers (XP) of the individual blocks and positions(AP′) identical to centers of the individual blocks of interest (theaverage of vector components V_(x) in the horizontal direction and theaverage of vector components V_(y) in the vertical direction) as themotion amount, and transmits the motion amount as data (hereinafter,this will be referred to as motion amount data) to the three-dimensionalimage generation unit 24.

The motion amount represents a value not only representing motion in ahorizontal motion direction (rotation direction) with respect to a faceon which the finger is placed but also representing motion in a verticalmotion direction (direction orthogonal to the rotation direction) withrespect to the face due to a variation in the finger pressure amount,the rotation axis, or the like.

Incidentally, instead of the average of individual position vectors (theaverage of vector components V_(x) in the horizontal direction and theaverage of vector components V_(y) in the vertical direction), forexample, a value (representative value) obtained from the individualposition vectors in accordance with a statistical method, such as themaximum value, the minimum value, or the standard deviation of theindividual position vectors, may be adopted as the motion amount.

In the motion amount calculation unit 23 in this embodiment, imagesobtained in the middle of the blood vessel extraction process (imagesafter the embossing processing is performed and before binarization isperformed) are adopted as images for which the motion amount is to becalculated.

In an image before the blood vessel extraction process is performed(image before the embossing processing is performed), blood vessels andthe other portions are clearly distinguished from each other, asdescribed above with reference to FIG. 7. The brightnesses of the bloodvessels in the image serve as information indicating the actualcross-section state, as shown in FIG. 9. However, this information iseliminated in an image after the blood vessel extraction process isperformed (image after binarizing processing is performed), as shown inFIG. 10. Thus, even if the cross sections of blood vessels differentfrom each other are shown, for example, as shown in FIGS. 11(A) and11(B), after the extraction process is performed, the different crosssections are likely to be made the same.

Therefore, if an image after the blood vessel extraction process isperformed (image after binarizing processing is performed) is adopted asan image for which the amount of displacement is to be calculated, in acase where a block having the brightness that is least different fromthe brightness of the block of interest ABL in the current image IM1 issearched for from the preceding image IM2 (FIG. 8(B)), many blocks eachhaving a brightness that is equal to or substantially equal to thebrightness of the block of interest ABL appear. Thus, a block RBL thattruly corresponds to the block of interest ABL cannot be found. As aresult, a situation in which the accuracy in the calculation of adisplacement amount is reduced may occur.

From the above description, in the motion amount calculation unit 23,images obtained in the middle of the blood vessel extraction process(images after the embossing processing is performed and beforebinarization is performed) are adopted as images for which a motionamount is to be calculated.

Note that although in general a plurality of blocks of interest in thecurrent image IM1 are all the pixels in the current image IM1, theplurality of blocks of interest may be end points, branch points, orinflection points of blood vessels reflected in the current image IM1,or some of these points.

In addition, although in general an area from which a block having thebrightness that is least different from the brightness of the block ofinterest ABL is searched for corresponds to the entire preceding imageIM2, the area may correspond to the size of a plurality of blocks ofinterest centered on a position displaced by a displace amount detectedpreviously. The shape of the area may be changed in accordance with theamount of temporal change in the displacement amount detectedpreviously.

(4-4) Three-Dimensional Image Generation Process

The three-dimensional image generation unit 24 detects, for individualblood vessel images captured from the circumference of a finger,silhouette regions of blood vessels captured in a projective space in acase where the blood vessels reflected in the individual images areprojected from viewpoints of the individual images to the projectivespace, and extracts a portion common to the individual detectedsilhouette regions as a stereoscopic image (three-dimensional volume) ofthe blood vessels.

The three-dimensional image generation unit 24 in this embodiment doesnot extract a portion common to silhouette regions projected in thedeepest area of a projective space as a stereoscopic image of bloodvessels. The three-dimensional image generation unit 24 is configured toextract a portion common to silhouette regions projected in an area fromthe surface of projection in a projective space to a projective planethat is distant from the surface of projection by a predetermined lengthin the depth direction as a stereoscopic image of blood vessels.

An example of a generation method by the three-dimensional imagegeneration unit 24 will be explained. As shown in FIG. 12, thethree-dimensional image generation unit 24 defines, as a projectivespace, a three-dimensional space having a predetermined shape includingcubes called voxels as constitutional units (hereinafter, this will bereferred to as a voxel space) (FIG. 13: step SP1).

Then, the three-dimensional image generation unit 24 generates, inaccordance with various values, such as the focal length and the imagecenter, stored in the ROM as camera information, a value stored in theROM as information defining the projective length from the surface ofprojection in the projective space in the depth direction, and a valueof motion amount data received from the motion amount calculation unit23, shape data of blood vessels from a plurality of image data items(binary blood vessel images) received from the blood vessel extractionunit 22.

That is, as shown in FIG. 14, the three-dimensional image generationunit 24 places, as a reference image, the binary blood vessel imagefirst received from the blood vessel extraction unit 22 at a positioncorresponding to a viewpoint having a rotation angle of 0[°] amongviewpoints around the voxel space, and detects a silhouette region ARprojected in an area from the surface of projection in the projectivespace to a projective plane that is distant from the surface ofprojection by a predetermined length L in the depth direction (in FIG.14, an area surrounded by solid lines) (FIG. 13: step SP2).Incidentally, in FIG. 14, a case where, in the object shown in FIG. 1,FIG. 1(A) represents a reference image is shown by way of example.

In a specific method for detecting a silhouette region, individualvoxels in the voxel space are reverse-projected to a reference image sothat projected points are calculated, and voxels whose projected pointsexist within the silhouette of blood vessels reflected in the referenceimage are caused to remain as a silhouette region.

Meanwhile, for each of the binary blood vessel images secondly andsubsequently received from the blood vessel extraction unit 22, thethree-dimensional image generation unit 24 identifies a motion amount ina rotation direction from the reference image to a binary blood vesselimage serving as the current processing target (hereinafter, this willbe referred to as a rotation motion amount), in accordance with motionamount data received from the motion amount calculation unit 23.

Then, the three-dimensional image generation unit 24 calculates therotation angle θ_(ro) of the binary blood vessel image serving as thecurrent processing target with respect to the reference image(hereinafter, this will be referred to as a first rotation angle) byusing the following equation:θ_(ro)=arctan(V _(x) /r)  (1),where the rotation motion amount is represented by V_(x) and a value setas the distance from the rotation axis of the finger to a blood vesselis represented by r, and determines whether or not the first rotationangle θ_(ro) is smaller than 360[°] (FIG. 13: step SP3).

In a case where the first rotation angle θ_(ro1) is smaller than 360[°](FIG. 13: “YES” in step SP3), this means a state in which all the viewvolumes (silhouette regions) of a plurality of binary blood vesselimages captured from the entire circumference of the finger have notbeen detected. In this case, the three-dimensional image generation unit24 calculates a difference between the first rotation angle θ_(ro) and arotation angle between the binary blood vessel image for which the viewvolume was detected immediately before the binary blood vessel imageserving as the current processing target and the reference image(hereinafter, this will be referred to as a second rotation angle), anddetermines whether or not the difference is equal to or greater than apredetermined threshold (FIG. 13: step SP4).

In a case where the difference is smaller than the threshold (FIG. 13:“NO” in step SP4), this means that the rotation of the finger is stoppedor in a state equal to stopping. In this case, the three-dimensionalimage generation unit 24 adopts, as a processing target, the binaryblood vessel image to be received immediately after the binary bloodvessel image serving as the current processing target, withoutcalculating a silhouette region of the binary blood vessel image servingas the current processing target. The three-dimensional image generationunit 24 is configured to prevent an ineffective silhouette region frombeing calculated, as described above.

In contrast, in a case where the difference is equal to or greater thanthe threshold (FIG. 13: “YES” in step SP4), this means a state in whichthe finger is rotated. In this case, the three-dimensional imagegeneration unit 24 places a binary blood vessel image IM_(X) serving asthe current processing target at a position corresponding to a viewpointVP_(X) having the rotation angle θ_(ro) with respect to a viewpointVP_(S) of a reference position IM_(S), for example, as shown in FIG. 15.

Then, after detecting, for the binary blood vessel image IM_(X), asilhouette region projected in an area from the surface of projection inthe projective space to a projective plane that is distant from thesurface of projection by a predetermined length in the depth direction(FIG. 13: step SP5), the three-dimensional image generation unit 24adopts the binary blood vessel image received immediately after thebinary blood vessel image as a processing target.

Note that in a case where the binary blood vessel image IM_(X) servingas the current processing target is placed around the circumference ofthe voxel space, the three-dimensional image generation unit 24identifies, for the binary blood vessel image IM_(X) and the binaryblood vessel image IM_((X-1)) for which the view volume was detectedimmediately before the binary blood vessel image IM_(X), the motionamount in a direction orthogonal to the rotation direction of the finger(the average of vector components V_(y) in the vertical direction of thebinary blood vessel image serving as the current processing target andthe binary blood vessel image that was most recently placed) inaccordance with motion amount data, and corrects the position of theviewpoint VP_(X) in a correction direction RD (direction parallel to theZ-axis direction in the voxel space) by the motion amount.

Consequently, even if a variation in the finger pressure amount or therotation axis occurs at the time of rotation of the finger, thethree-dimensional image generation unit 24 is capable of detecting asilhouette region while following the variation. Thus, compared with acase where the motion amount in the direction orthogonal to the rotationdirection of the finger is not taken into consideration, thethree-dimensional image generation unit 24 can detect a silhouetteregion accurately.

In this manner, the three-dimensional image generation unit 24sequentially detects silhouette regions of blood vessels reflected inbinary blood vessel images until a binary blood vessel image in whichthe first rotation angle θ_(ro) with respect to the reference image isequal to or greater than 360[°] serves as the current processing target(FIG. 13: loop including steps SP3-SP4-SP5).

Here, for example, as shown in FIG. 16, silhouette regions are detectedwithin areas from the surface of projection in the voxel space(projective space) to a projective plane that is distant from thesurface of projection by a predetermined length in the depth direction(areas surrounded by solid lines). Thus, in a case where attention ispaid to an image on the front side of the object in FIG. 1 (FIG. 1(A))and an image on the back side of the object (FIG. 1(B)), even ifportions in which view volumes are not the same exist in the voxelspace, voxels of projection portions (silhouette regions) of the objectin the individual images remain.

Therefore, in a case where a binary blood vessel image in which thefirst rotation angle θ_(ro) with respect to the reference image is equalto or greater than 360[°] serves as the current processing target, inthe voxel space, for example, as shown in FIG. 17, a common portion(solid line portion) of voxels remaining as projection portions(silhouette regions) of the object in the individual images is expressedas a true stereoscopic image (three-dimensional volume) of blood vesselsof the actual object. Incidentally, in FIG. 16, a column region portionrepresents voxles remaining as a non-projection portion.

In a case where a binary blood vessel image in which the first rotationangle θ_(ro) with respect to the reference image is equal to or greaterthan 360[°] serves as the current processing target, thethree-dimensional image generation unit 24 identifies voxels having thecommon portion as a stereoscopic image of blood vessels, and extractsvoxel data as data of the stereoscopic image. The voxel data isregistered as registration data in the memory 13 in the blood vesselregistration mode, and is verified against registration data registeredin the memory 13 in the authentication mode.

(5) Operation and Effect

With the configuration described above, the control unit 10 (thethree-dimensional image generation unit 24) in the authenticationapparatus 1 sequentially receives a plurality of binary blood vesselimages captured from the circumference of a finger and obtained whenblood vessels in the captured images are extracted.

In addition, the three-dimensional image generation unit 24 detects, forthe individual binary blood vessel images, projection regions projectedin an area from the surface of projection in a voxel space to aprojective plane that is distant from the surface of projection by apredetermined length in the depth direction in a case where an objectreflected in the individual images is projected to the voxel space fromviewpoint positions of the individual images (for example, see FIG. 14),and extracts a portion common to the individual detected projectionregions (see FIG. 17).

The three-dimensional image generation unit 24 does not extract aportion common to silhouette regions projected in the deepest area ofthe voxel space as a stereoscopic image of blood vessels. Thethree-dimensional image generation unit 24 extracts a portion common tosilhouette regions projected to an area from the surface of projectionin the voxel space to a projective plane that is distant from thesurface of projection by a predetermined length in the depth directionas a stereoscopic image of blood vessels. Thus, the view volume can becalculated while attention is paid to an area corresponding to the depthfrom the surface of the finger to an image pickup target (blood vessel)inside the finger.

Consequently, even in a case where view volumes are not the same amongregions from the surface of a blood vessel to the opposite side, as longas view volumes near the surface of the blood vessel are the same, thethree-dimensional image generation unit 24 causes the common portion toremain as voxels of a projection portion (silhouette region) of theblood vessel. In this manner, even in a case where a blood vesselportion existing on the back side of an image pickup surface cannot beprojected, the shape that truly reflects the actual blood vessel can beexpressed (for example, see FIG. 15).

With the configuration described above, since a portion common tosilhouette regions projected in an area from the surface of projectionin a projective space to a projective plane that is distant from thesurface of projection by a predetermined length in the depth directionis extracted as a stereoscopic image of a blood vessel, theauthentication apparatus 1 that is capable of generating the shape of ablood vessel with high accuracy even in a situation in which an image ofthe back side of the blood vessel cannot be captured, can be realized.

(6) Other Embodiments

In the embodiment described above, a case where a blood vessel inside aliving body is used as an image pickup target has been described.However, the present invention is not limited to this. For example, anerve or a fingerprint, the face, or the like on the surface of a livingbody may be used as an image pickup target. Alternatively, an objectother than a living body may be used. Note that embossing processing maybe omitted in an appropriate manner in accordance with an image pickuptarget used.

In addition, in a case where an image pickup target inside a livingbody, such as a nerve or a blood vessel, is used, although a case wherea finger is used as a living body portion has been described in theforegoing embodiment, the present invention is not limited to this. Forexample, a portion, such as the palm of a hand, a toe, an arm, an eye,or an arm, may be used as a living body portion.

In addition, although projection regions to be detected, the projectionregions being projected in a projective space in a case where an objectreflected in images is projected to the projective space from viewpointpositions of the individual images, are fixed in the foregoingembodiment, the present invention may vary the projection regions to bedetected.

That is, in the foregoing embodiment, a value (fixed value) representinga projective length from the surface of projection in the projectivespace in the depth direction is stored in the ROM. However, instead ofthis, for example, information representing the correspondence betweenthe body fat percentage and the projective length is stored.

Prior to detecting a silhouette region of the first received image(reference image) (FIG. 13: step SP2), the control unit 10 causes thenotification unit 15 to issue an instruction to enter the body fatpercentage of a user whose image is to be captured. Then, the controlunit 10 detects the body fat percentage entered from the operation unit11, and sets a value corresponding to the detected body fat percentage.Accordingly, the control unit 10 changes the projective length.

By performing the processing described above, in a case where asilhouette region projected in an area from the surface of projection ina voxel space to a projective plane that is distant from the surface ofprojection by a predetermined length in the depth direction is detected,for a blood vessel which is likely to become more difficult to projectas the body fat percentage increases, the view volume can be obtainedwhile attention is paid to a region corresponding to the depth from thesurface of a finger to an image pickup target (blood vessel) inside thefinger, irrespective of an individual difference in the body fatpercentage. Thus, the shape that more truly reflects the actual bloodvessel can be expressed.

Note that instead of entering the body fat percentage of a user whoseimage is to be captured, information on the living body, such as theheight, weight, and age, may be entered so that the body fat percentagecan be calculated from the entered information. A set value may beassociated with various factors, such as the finger diameter and theweight, as well as the body fat percentage.

In addition, for example, instead of a value representing the projectivelength in the depth direction from the surface of projection in theprojective space, information representing the correspondence between aviewpoint and a value representing the projective length is stored inthe ROM. Prior to detecting a silhouette region of the first receivedimage (reference image) (FIG. 13: step SP2), the control unit 10 detectsa viewpoint corresponding to a blood vessel image in accordance with thefinger width of a finger silhouette reflected in a blood vessel image,information on the inside of the finger silhouette reflected in a fingerimage, and the like, and sets a value corresponding to the detectedviewpoint. Accordingly, the control unit 10 changes the projectivelength.

By performing the processing described above, in a case where asilhouette region projected in an area from the surface of projection ina voxel space to a projective plane that is distant from the surface ofprojection by a predetermined length in the depth direction is detected,a projective length corresponding to the depth from the surface of thefinger to a position at which a blood vessel exists can be set for eachof the dorsal side of the finger and the ventral side of the finger.Hence, the shape that more truly reflects the actual blood vessel can beexpressed.

As described above, prior to detection of a silhouette region of thefirst received image (reference image), a setting step of detectinginformation on an image pickup target and setting a predetermined lengthcorresponding to the detected information is provided, and a projectionregion projected in an area from the surface of projection in aprojective space to a projective plane that is distant from the surfaceof projection by the predetermined length set in the setting step in thedepth direction is detected. Therefore, the shape of a blood vessel canbe generated with higher accuracy.

Furthermore, although a case where the blood vessel registration modeand the authentication mode are executed in accordance with a programstored in the ROM has been described in the foregoing embodiment, thepresent invention is not limited to this. The blood vessel registrationmode and the authentication mode may be executed in accordance with aprogram acquired by being installed from a program storage medium, suchas a CD (Compact Disc), a DVD (Digital Versatile Disc), or asemiconductor memory, or being downloaded from a program providingserver on the Internet.

Furthermore, although a case where the control unit 10 performsregistration processing and authentication processing has been describedin the foregoing embodiment, the present invention is not limited tothis. Part of the processing may be performed by a graphics workstation.

Furthermore, a case where the authentication apparatus 1 that has animage pickup function, a verification function, and a registrationfunction is used has been described in the foregoing embodiment, thepresent invention is not limited to this. The present invention may beapplied to an embodiment in which each function or part of each functionis assigned to a corresponding single apparatus in accordance with theapplication.

INDUSTRIAL APPLICABILITY

The present invention is useful in the area of biometricsauthentication.

EXPLANATION OF REFERENCE NUMERALS

1: authentication apparatus, 10: control unit, 11: operation unit, 12:image pickup unit, 13: memory, 14: interface, 15: notification unit, 15a: display section, 15 b: sound output section, 21: image rotation unit,22A: embossing section, 22B: binarizing section, 23: motion amountcalculation unit, 24: three-dimensional image generation unit, 25: shapeextraction unit

The invention claimed is:
 1. An object-shape generation method, comprising: in an apparatus: capturing a plurality of images of a first object within a second object using near infrared light rays; capturing a plurality of images of the second object using visible light rays; extracting a plurality of silhouette points of the second object from the plurality of images on the second object; determining a set of reference points from the plurality of extracted silhouette points; detecting an angle of the set of reference points in relation to a reference line in a transverse direction of the plurality of images of the second object; aligning one or more of the plurality of images of the first object with the plurality of images of the second object based on the detected angle; detecting a plurality of projection regions of the first object when individual images of the plurality of images of the first object are projected to a projective space from different viewpoints of the individual images, the individual images being captured from a circumference of the second object; wherein the projection regions are projected in an area from a surface of projection in the projective space to a projective plane that is distant from the surface of projection by a predetermined length in a depth direction; and extracting a common portion of the plurality of detected projection regions.
 2. The object-shape generation method according to claim 1, further comprising: calculating, from one of the individual images, an amount of movement in a rotation direction of the first object in an image captured prior to the one of the individual images, wherein the calculating comprises: obtaining a rotation angle of a detection target image with respect to a reference image from an amount of movement between the reference image and the detection target image; and detecting a projection region of the plurality of projection regions when the first object in the detection target image is projected to the projective space from a viewpoint position having the rotation angle with respect to a viewpoint position of the reference image.
 3. The object-shape generation method according to claim 1, further comprising: calculating, from one of the individual images, a movement amount in a direction orthogonal to a rotation direction of the first object in an image captured prior to the one of the individual images; and correcting a viewpoint position of the one of the individual images in a correction direction by the movement amount.
 4. The object-shape generation method according to claim 1, further comprising: detecting information on an image pickup target; setting the predetermined length based on the detected information; and detecting the plurality of projection regions projected in an area from a surface of projection in the projective space to a projective plane that is distant from the surface of projection by a set predetermined length in a depth direction.
 5. The object-shape generation method according to claim 1, further comprising storing, in a memory, a value representing the predetermined length from the surface of projection in the projective space in the depth direction.
 6. The object-shape generation method according to claim 1, further comprising performing embossing processing on each of the plurality of images of the first object using a differentiation filter to emboss the first object on each of the plurality of images of the first object.
 7. The object-shape generation method according to claim 6, further comprising converting each of a plurality of embossed images into a binary image with reference to a set brightness.
 8. An object-shape generation apparatus comprising: a work memory; and an image processing unit that executes image processing by using the work memory, wherein the image processing unit comprises one or more processors operable to: capture a plurality of images of a first object within a second object using near infrared light rays; capture a plurality of images of the second object using visible light rays; extract a plurality of silhouette points of the second object from the plurality of images of the second object; determine a set of reference points from the plurality of extracted silhouette points; detect an angle of the set of reference points in relation to a reference line in a transverse direction of the plurality of images of the second object align one or more of the plurality of images of the first object with the plurality of images of the second object based on the detected angle; detect a plurality of projection regions of the first object when individual images of the plurality of images of the first object are projected to a projective space from different viewpoints of the individual images, the individual images being captured from a circumference of the second object; wherein the projection regions are projected in an area from a surface of projection in the projective space to a projective plane that is distant from the surface of projection by a predetermined length in a depth direction; and extract a common portion of the plurality of detected projection regions.
 9. A non-transitory computer-readable medium having stored thereon a computer program having at least one code section for communication, the at least one code section being executable by a computer for causing the computer to perform steps comprising: capturing a plurality of images of a first object within a second object using near infrared light rays; capturing a plurality of images of the second object using visible light rays; extracting a plurality of silhouette points of the second object from the plurality of images of the second object; determining a set of reference points from the plurality of extracted silhouette points; detecting an angle of the set of reference points in relation to a reference line in a transverse direction of the plurality of images of the second object; aligning one or more of the plurality of images of the first object with the plurality of images of the second object based on the detected angle; detecting a plurality of projection regions of the first object when individual images of the plurality of images of the first object are projected to a projective space from different viewpoints of the individual images, the individual images being captured from a circumference of the second object; wherein the projection regions are projected in an area from a surface of projection in the projective space to a projective plane that is distant from the surface of projection by a predetermined length in a depth direction; and extracting a common portion of the plurality of detected projection regions. 